Telephone system.



J. G. MITCHELL. TELEPHONE SYSTEM. 7

APPLICATION FILED AUG. 8, 1908.

1,025,477. PatentedMayZ1912.

. a sums-8mm 1.

mmmmml a -J. MITCHELL.

TELEPHONE SYSTEM. APPLIUATION FILED AUG. a, 1908.

3 SHEEN-SHEET 2.

i I nuonkoz Jag 8m? Wane/4am Patented May 7, 1912.

J. G, MITCHELL.

TELEPHONE SYSTEM.

. APPLIO ATION I'ILED AUG. 8, 1903. 1,025,477.

Patented May 7, 1912.

3 SHEETS-SHEET 3.

l o awwmroz wikuwoe'o COLUMBIA PLANoGRAPu 60., WASHINGTON, D. c

UNITED STATES PATENT OFFICE.

JAY GORDON MITCHELL, OF CLEVELAND, OI-IIO, .ASSIGNOR TO THE NORTH ELECTRIC COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

TELEPHONE SYSTEM.

Patented May *7, 1912.

Application filed August 8, 1908. Serial No. 447,583.

State of Ohio, have invented certain new and useful Improvements in Telephone Systems, of which the following is a specification, reference being had therein to the accompanying drawing.

My invention relates to telephone systems, and especially to trunking circuits for the same.

It has for its object the provision of improved means for trunk signaling and for supervising alltrunk connections.

Briefly stated, my invention comprises a metallic circuit trunk line extending be tween an A operator and a B operator, provided at the B end with a pair of condensers, one in each limb, a signal magnet normally bridged across the trunk through the back contact of a cutoff relay, so as to include one of the condensers, and a supervisory relay having two windings, one permanently bridged around one condenser and the other bridged through the front contact of the cut-off relay around'the other condenser; the cut-off relay having its circuit closed through the contacts of the trunk plug when inserted in a jack by the B operator, and the supervisory relaycontrolling a signal device. The trunksignal inaddition to its actuating winding has a second a holding or looking winding closed when it is energized and controlled by a contact -perated by a listening key and keyfor holding the trunk.

Other features of the invention will fully appear from the following description and appended claims.

Referring to the accompanying drawings, Figure 1 shows a subscribers station, an A operators cord circuit, and the terminal of an outgoing trunk adapted to be connected through said cord circuit with a subscribers line. Fig. 2 shows the circuits at the B end of the trunk, and a terminal of a subscribers line similar to that in Fig. 1. Fig. 3 is a simplified diagram of the circuits of Fig. 2.

Referring to Fig. 1, A is a subscribers station with a line circuit 12 extending to the central oflice where it terminates on a jack J, and is provided with a line relay L and a signal L" controlled thereby. This circuit arrangement may be varied, as it forms no part of the present invention, and it will be noted that multiple jacks may be employed although they are not herein shown. A line circuit is adapted to be con nected to other lines by means of the plugs P, P connected by a cord circuit having listening and ringing keys Q, Q, and double wound bridged supervisory relays S, S separated by condensers C, C, so that current fromthe main battery M will flow in both directions over the cord to the respective lines. J is a trunk jack forming a terminal of an outgoing trunk to another switchboard or exchange. This has tip, ring and sleeve contacts to cooperate with the re spective contacts of the plug P.

Referring now to Fig. 2, the trunk conductors 3t extend to the B exchange, where they are connected through the contacts of the night service key D and the condensers C, C to the plug P. A combined listening and ringing key Q Q is provided in the trunk, also a key Q for holding con nection of the trunk at central and a guard lamp 9* controlled by this key. The trunk calling signal is indicated at S and the supervisory signal at S The calling signal is directly controlled through the trunk by means of its winding 8 bridged from point 5 at the condenser C through thenormally closed back contact of the cut-off relay R to the point 6 at the condenser 0 The holding winding 8 is provided on the signal, closed when it is actuated, and controlled by contacts of the listening key Q and the holding key Q The supervisory signal S is controlled by the double wound relay B, one of whose windings r is bridged from the point 7 at condenser C to the point 5 on the other side of the same; while the other winding 1 is similarly bridged when the relay R is energized, from the point 6 at condenser C to the point 8 on the other side of the same. The circuit connections of these various pieces of apparatus, and their functions, will particularly appear from the following statement of operation:

Assuming that subscriber A has called for connection with a subscriber in the branch or B exchange (as for example subscriber A in Fig. 2), the A operator answers by inserting the plug P in the calling line jack, and hav-' ing ascertained the number wanted, inserts the plug P in the trunk ack, and rings out over the trunk. Current from her generator passes through the following circuit: trunk wire 3 to the contacts of key D (Fig. 2), wire 9, winding 8', wire 10, normally closed contact 1, wire 11, point 6, through the condenser C wire 12, contacts of key D, trunk wire 4: and back to the A exchange. This current energizes the signal S whose magnet in pulling up its armature closes the following circuit of the winding 8 from the frame at 13 to the windings 8 wire 14:, closed contacts of key Q}, wire 15, closed contacts of key Q and wire 16 to battery. The signal remains displayed after'the ringing ceases. The B operator uses the listening key Q and ascertains the number wanted, breaking the circuit of the holding winding s and restoring the signal S at the same time. She then inserts the plug P in the wanted jack and by means of her ringing key Q sends out ringing current by the following path: generator G (indicated by letter only), key Q wire 16, closed contacts of key D, wire 17 to the tip of the plug P and subscribers line back to the ring of the plug wire 18, closed contacts of the key D, wire 19 to the key Q and back to the generator. After the connection is complete and the called subscriber has. answer, the supervisory relay R controlling the signal S is itself controlled over the following circuit: Current flows from the central office at the A end of the trunk over the trunk wire 3, contacts of key D, wire 9, to the point 5, wire 20, to winding 7" of the supervisory relay, wire 21, to point 7 wire 22, closed contacts of key Q wire 16, closed contacts of key D, wire 17 to tip of the plug and subscribers line to station A and back through the ring by wire 18, contacts of key D, wire 19, contacts of key Q wire 23, point 6, Wire 11, contact r of relay R (which is closed as long as the plug 1 is in the line jack), wire 24, winding 1" of relay R, wire 25, point 8, wire 12, closed contacts of key D, trunk wire 4 and back to the central ofiice. As long as the called subscriber has his receiver off the hook and his line circuit thereby closed, the relay R pulls up, and maintains the circuit of the supervisory signal open, this circuit being as follows: from main battery M, wire 28, contact 0 of cutoff relay R, wire 29, contact 9 of relay R, wire 30, supervisory relay and back to battery. When the subscriber hangs up the contact 7 is closed and the supervisory signal is displayed.

The holding key Q when actuated closes the circuit of the guard lamp 9 as follows: Main battery M, wire 31, key Q wire 32, lamp 9 wire 33 and back to battery. It also bridges across the trunk a coil H, which serves to maintain the trunk circuit closed so far as the A operator is concerned, the

connections being as follows: Trunk wire 3, key D, wire 9, point 5, wire 34, coil H, wire 35, key Q}, wire 26, point 8, key D, trunk wire 1 and back to central ofiice. The guard lamp keeps the B operator advised that the trunk is being held, and when the plug P is withdrawn the cut-off relay R lets go and all the other parts are restored to normal.

Fig. 3 shows schematically the relation of the parts without the complication of Fig. 2, all keys being omitted. The magnets and relays are marked the same as in Fig. 2 and further description thereof is deemed unnecessary.

It is obvious that many changes in detail may be made in this circuit and in the apparatus employed therein without departing from the invention, and I wish it understood that all such changes are contemplated by me as fairly fall within the scope of the appended claims.

Having thus described my invention what I claim and desire to secure by Letters Patent is 1. A trunk signaling circuit for telephone exchanges, having a metallic circuit trunk line with a condenser at the B end in each limb and a supervisory relay having windings bridged around said condensers, together with a signal controlled by said relay, whereby current over the trunk line may pass through to a called subscribers line for purposes of supervision.

2. A trunk signaling system for telephone exchanges comprising a metallic circuit trunk line deriving current from an A operators cord circuit, a pair of condensers at the B end, one in each side of the trunk, and a supervisory relay having two windings, each connected around one of the condensers, together with means at a subscribers station for controlling the flow of current in his line and a signal controlled by said supervisory relay.

3. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, condensers in opposite sides of the said trunk, and an advance signal connected from a point on the B side of one condenser to a point on the A side of the other, together with a source of periodic signaling current associated with the A operators cord circuit, whereby said advance signal may be actuated by the A operator, but will remain irresponsive to direct current flow in any portion of the trunk.

t. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of direct current and a supervisory signal responsive thereto connected with the cord circuit at the A position, a holding key in the trunk at the B position, and means controlled in the actuation of said holding key to disable the A supervisory signal.

5. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position,a source of direct current and a supervisory signal responsive thereto connected with the cord circuit at the A position, a holding key in the trunk at the B position, means controlled in the actuation of said holding key to disable the A supervisory signal, so as to hold the trunk, and a guard signal also controlled in the actuation of said key to indicate that the trunk is being held.

6. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of direct current and a supervisory signal at the A position responsive to the current flow from said source in the cord and trunk when conjoined, a holding key in the trunk at the B position, and a-short circuiting device adapted to be bridged across the trunk 011 the actuation of said key in order to hold the trunk and prevent the eltective display of said supervisory signal.

7. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of current and a supervisory signal at the A position responsive to current flow from said source in the cord and trunk when conjoined, a holding key in the trunk at the B position, and a coil adapted to be bridged by said key across the trunk so as to short circuit the same and maintain the A supervisory signal undisplayed, thereby holding the trunk.

8. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, A B operators position containing callingterminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of curent and a supervisory signal at the A position responsive to current flow from said source in the cord and trunk when conjoined, a holding key in the trunk at the B position, a coil adapted to be bridged by said key across the trunk so as to short circuit the same and maintain the A supervisory signal undisplayed, thereby holding the trunk, and a guard signal adapted to be displayed when the key is actuated, to show that the trunk is being held.

9. In a telephone exchange system, subscriberslines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of direct current and a supervisory signal both associated with the A cord circuit, said signal being responsive to current flow fronrthe source through the cord and the trunk when conjoined, and a supervisory signal at the B position connected to the trunk so as to maintain the balance thereof while taking current in series from the A source through the A supervisory signal and the called subscribers line, whereby simultaneous indications of the state of a connection are afforded at both A and B positions.

10. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plurality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a source of current and a supervisory signal responsive thereto in the A cord circuit, inductive means maintaining the continuity of the trunk at the B position, and a supervisory signal connected in shunt of said inductive means, whereby current supply for the called subscribers line will pass from the A source through both the A and the B supervisories in series, with the consequent simultaneous control of both by the called subscriber.

11. In a telephone exchange system, subscribers lines, an A operators position containing answering terminals for a plnrality of lines, a B operators position containing calling terminals for a plurality of lines, a cord circuit at the A position adapted to cooperate with the line terminals, a trunk line extending from the A to the B position, a

ringing generator at the A position, a signal device at the 13 position responsive to current from said generator through the trunk, self-locking means adapted to maintain said signal displayed after its initial actuation by said ringing current, and unlocking means for the same controlled by the B operator in the use of her listening key.

12. A telephone exchange system including telephone lines extending from sub-stations to one exchange, telephone lines ex tending from sub-stations to a second exchange, a trunk circuit extending between said exchanges and having operator-controlled means at the first exchange for connecting it with telephone lines extending to the first exchange, link circuits at the second exchange for uniting lines extending thereto, clearing-out or supervisory signaling apparatus associated with said link circuits, and operator-controlled means at the first exchange for preventing the operation of said supervisory or clearing-out signaling apparatus at the second exchange.

In testimony whereof I aflix my signature in presence of two itnesses,

JAY GORDON MITCHELL. Vitnesses CHAs. HTUTY, GEO. C. STEELE.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents. Washington, I). G. 

